Loop integrity test device and method for digital subscriber line (xDSL) communication

ABSTRACT

A digital subscriber line (xDSL) communication system ( 10 ) is disclosed that allows xDSL communication across a local loop. The system ( 10 ) includes a local loop termination point ( 14 ) and customer premises equipment ( 12 ) connected to a twisted pair telephone line ( 16 ). Loop integrity test devices ( 22, 24 ) for xDSL communication are located at the local loop termination point ( 14 ) and the customer premises equipment ( 12 ) and are coupled to the telephone line ( 16 ). The loop integrity test devices ( 22, 24 ) are respectively operable to transmit test signatures across the telephone line ( 16 ), to receive and evaluate test signatures from the telephone line ( 16 ), and to indicate whether the telephone line ( 16 ) can support xDSL communication based upon evaluation of test signatures.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of U.S. application Ser. No.08/929,778, filed Sep. 15, 1997, by James R. Sisk and John F. McHale,entitled “Loop Integrity Test Device and Method for Digital SubscriberLine (xDSL) Communication”.

TECHNICAL FIELD OF THE INVENTION

[0002] This invention relates in general to data communication, and moreparticularly to a loop integrity test device and method for digitalsubscriber line (xDSL) communication.

BACKGROUND OF THE INVENTION

[0003] Digital subscriber line (xDSL) communication can provide a highbandwidth data path supported by the twisted pair wiring infrastructureof the public switched telephone network (PSTN). xDSL technologiessupport data service simultaneously with traditional telephone serviceusing a separation technique. Suitable xDSL technologies includeasymmetric digital subscriber line (ADSL), rate adaptable digitalsubscriber line (RADSL), symmetric digital subscriber line (SDSL),high-speed digital subscriber line (HDSL) and very high-speed digitalsubscriber line (VDSL).

[0004] In general, an xDSL communication link is established across thelocal loop between customer premises equipment (CPE) and the local looptermination point (e.g., central office or remote terminal). The localloop termination point typically has a xDSL access multiplexer (DSLAM)that handles the XDSL link on the network side, and the CPE typicallyincludes one or more xDSL termination units (XTU) that handle the xDSLlink on the customer premises side. One architecture for xDSLcommunication is disclosed in U.S. Pat. No. 5,668,857 (Ser. No.08/625,769), filed Mar. 29, 1996, by John F. McHale, and entitled“Communication Server Apparatus and Method.”

[0005] In order to support xDSL communication, the twisted pair line onthe local loop between the customer premises and the loop terminationpoint must meet certain physical characteristics. If it does not, anxDSL communication link can not be successfully established.Consequently, it can be desirable to allow the xDSL capability of thelocal loop to be quickly verified at the same time that xDSL service isinstalled at the customer premises. Further, it can be desirable tomonitor the xDSL capability of the local loop on an ongoing andcontinuous basis.

SUMMARY OF THE INVENTION

[0006] In accordance with the present invention, a loop integrity testdevice and method for digital subscriber line communication aredisclosed that provide advantages over conventional xDSL communicationdevices and systems.

[0007] According to one aspect of the present invention, a digitalsubscriber line (xDSL) communication system allows xDSL communicationacross a local loop. The system includes a local loop termination pointand customer premises equipment connected to a twisted pair telephoneline. Loop integrity test devices for xDSL communication are located atthe local loop termination point and the customer premises equipment andare coupled to the telephone line. The loop integrity test devices arerespectively operable to transmit test signatures across the telephoneline, to receive and evaluate test signatures from the telephone line,and to indicate whether the telephone line can support xDSLcommunication based upon evaluation of test signatures.

[0008] According to another aspect of the present invention, a loopintegrity test device is disclosed that includes a line interface unitoperable to connect to and interface with a twisted pair telephone line.The test device also includes an output device operable to indicate apass state and a fail state. Further, the test device includes a controlunit having a generation unit and an evaluation unit. The generationunit is operable to transmit a test signature across the telephone line.The evaluation unit is operable to receive and evaluate a test signatureto determine whether the telephone line can support xDSL communication.The control unit is then operable to direct the output device toindicate a pass state if the telephone line can support DSLcommunication and to indicate a fail state if the telephone line can notsupport xDSL communication.

[0009] A technical advantage of the present invention is that theintegrity of the local loop can be verified at the time of installationof high speed xDSL data service at a customer premises. In particular,the present loop integrity test device provides an immediate indicationof whether the loop can support xDSL communication when it is installed.

[0010] Another technical advantage of the present invention is animprovement in the reliability and monitoring of the xDSL communicationsystem. The test devices implement a continuous integrity check of thelocal loop that allows the telephone company or other service providerto be alerted to a problem on the local loop. This notification mayallow the service provider to correct the problem before a degradationof service is noticed by the customer.

[0011] Other technical advantages should be readily apparent to oneskilled in the art from the following figures, description, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] For a more complete understanding of the present invention, andfor further features and advantages, reference is now made to thefollowing description taken in conjunction with the accompanyingdrawings, in which:

[0013]FIG. 1 is a block diagram of one embodiment of an xDSLcommunication system having loop integrity test devices for xDSLcommunication according to the present invention;

[0014]FIG. 2 is a block diagram of one embodiment of a loop integritytest device for xDSL communication according to the present invention;and

[0015]FIG. 3 is a flow chart of a method for local loop integritytesting for xDSL communication according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0016]FIG. 1 is a block diagram of one embodiment of an xDSLcommunication system, indicated generally at 10, having loop integritytest devices for xDSL communication according to the present invention.System 10 includes customer premises equipment 12 that can be located atany one of a number of customer premises. System 10 also includes alocal loop termination point 14 which is connected to customer premisesequipment 12 via a twisted pair telephone line 16. Customer premisesequipment 12 typically includes a network interface device (NID) 18which forms a physical interface between the customer premises and thetelephone network as well as any other equipment located at the customerpremises or other remote loop termination point. Local loop terminationpoint 14 can be a central office, remote terminal or other appropriatetermination of the local loop and can include an xDSL access multiplexer(DSLAM) 20 that provides xDSL high bandwidth data service. Telephoneline 16 supports conventional voice traffic and is intended to supportxDSL communications. However, depending upon physical characteristics oftelephone line 16, it may not support xDSL communication or may onlysupport limited xDSL communication. For example, the distance of thelocal loop, any splices in telephone line 16, loading on telephone line16 and other physical characteristics affect the integrity of telephoneline 16 for xDSL communication.

[0017] According to the present invention, a loop integrity test device22 is located at customer premises equipment 12, and a loop integritytest device 24 is located at local loop termination point 14. Both loopintegrity test devices 22 and 24 are coupled to telephone line 16. Loopintegrity test devices 22 and 24 respectively operate to transmit testsignatures across telephone line 16 and to receive and evaluate a testsignature from telephone line 16. The test signature can be a signalwith implanted high frequency tones, DC voltages or other distinctivecharacteristics and can be transmitted periodically at some timeinterval. For example, the test signature can be pulses, tones,modulated tones, xDSL symbols (e.g., Quadrature Amplitude Modulated(QAM) symbols or Discrete Multitone (DMT) symbols), or other xDSLphysical layer symbols chosen to allow determination of the linecharacteristics and the ability of the line to support xDSLcommunication. Based upon evaluations of the test signature, loopintegrity test devices 22 and 24 indicate whether telephone line 16 cansupport DSL communication. In this manner, loop integrity test devices22 and 24 both provide an initial indication of the line integrity uponinstallation as well as provide an ongoing monitoring of the lineintegrity.

[0018] In one implementation, loop integrity test devices 22 areinstalled in network interface device (NID) 18 at the customer premises.This is done for ease of installation by a service provider and to avoidinterference with other customer premises equipment 12 located behindnetwork interface device (NID) 18. Also, in this implementation, loopintegrity device 24 is installed separate from DSL access multiplexer 20at local loop termination point 14. Similarly, this is done to avoidinterference with DSL access multiplexer 20. It should be understoodthat other implementations are possible within the scope of the presentinvention. For example, loop integrity device 22 can be implemented aspart of other equipment at the customer premises or loop terminationpoint 14 such as part of an xDSL termination unit.

[0019]FIG. 2 is a block diagram of one embodiment of a loop integritytest device, indicated generally at 30, for xDSL communication accordingto the present invention. As shown, test device 30 can comprise a lineinterface unit 32 that connects to a telephone line 34. Line interfaceunit is coupled to a control unit 36 which can comprise a test signaturegeneration unit 38 and a test signature evaluation unit 40. Controldevice 36 is, in turn, coupled to an output device 42. Output device 42can, for example, comprise light emitting diode (LED) devices, an LCDdisplay, a speaker, a register, an electronic signal output or acombination of thereof.

[0020] In operation, line interface unit 32 provides an interfacebetween control unit 36 and telephone line 34. Control unit 36 managesthe operation of test device 30 and directs output device 42. Withincontrol unit 36, generation unit 38 periodically generates and transmitsa test signature through line interface unit 32 and across telephoneline 34. Generation unit 38 can, for example, generate a test signatureby obtaining one from local storage or based upon a generationalgorithm. Once generated, the test signature is transmitted to theopposite end point of the local loop. When test device 30 is located ata local loop termination unit, the test signature is transmitted to testdevices located at customer premises. Conversely, when test device 30 islocated at the customer premises, the test signature is transmitted tothe local loop termination equipment. The test signature is designedsuch that pertinent physical characteristics of telephone line 34 can bedetermined from analysis of changes to the test signature after it hastraveled across telephone line 34. In general, xDSL communication issensitive in that it uses higher frequencies across the twisted paircooper lines, thus physical characteristics such as impedance and linelength are important to the integrity of telephone line 34.

[0021] Evaluation unit 40 receives test signatures transmitted acrosstelephone line 34 and evaluates the test signatures to determine whethertelephone line 34 can support some level of xDSL communication. Theevaluation can assess such things as loss of energy, change in bitstream pattern, and other changes of the test signature. Based uponanalysis of the test signature, evaluation unit 40 identifies whethertelephone line 34 can support xDSL communication. Evaluation unit 40 canthen direct output device 42 to provide an indication based upon theresults of the evaluation. In particular, if telephone line 34 cansupport xDSL communication, then a pass state can be indicated. If not,then a fail state can be indicated. The indication can, for example,take the form of an audible alarm, a visual display, an electronicmessage or an electronic signal. In one implementation, output device 52can provide an electronic flag to software such that automated loopmonitoring can be established at the local loop termination point.

[0022]FIG. 3 is a flow chart of a method for local loop integritytesting for xDSL communication according to the present invention. Asshown, in step 50, a test signature is transmitted across the local looptelephone line to be tested. In step 52, the test signature is receivedat the opposite end of the local loop. The received test signature isthen evaluated, in step 54, to determine whether the telephone line cansupport xDSL communication. This determination is accomplished basedupon changes to the test signature caused by transmission across thetelephone line. Then, in step 56, an indication is made whether thetelephone line can support xDSL communication.

[0023] According to the present invention, instant verification of loopintegrity for xDSL communication across the local loop can be obtainedat install time. This functionality can be accomplished using loopintegrity test devices that can be loop powered. Once installed, thetest devices can also provide continuous monitoring of the loop (i.e.,twenty-four hours a day, seven days a week) and can provide bothhardware and software alarms to the customer premises and to the serviceprovider. The test devices are relatively low in cost and provideimportant qualification of the local loop for spectral compatibility andloop viability for xDSL communication.

[0024] Although the present invention has been described with severalembodiments, a myriad of changes, variations, alterations,transformations, and modifications may be suggested to one skilled inthe art, and it is intended that the present invention encompass suchchanges, variations, alterations, transformations, and modifications asfall within the spirit and scope of the appended claims.

What is claimed is:
 1. A loop integrity test device for digitalsubscriber line (xDSL) communication systems, the test devicecomprising: a line interface unit operable to connect to and interfacewith a first point on a twisted pair telephone line, the telephone lineforming a continuous electrically conductive path without intermediatecomponents between the first point and a second point; an output deviceoperable to indicate a pass state and a fail state; and a control unitcomprising: a generation unit operable to transmit a first testsignature across the telephone line for reception and evaluation at thesecond point, the transmission of the first test signature initiating afirst loop integrity test; and an evaluation unit operable to receive asecond test signature transmitted across the telephone line, the secondtest signature originally generated independent of the first testsignature by a second loop integrity test device to initiate a secondloop integrity test, the evaluation unit further operable to evaluatethe second test signature to determine whether the telephone line cansupport xDSL communication; the control unit operable to direct theoutput device to indicate a pass state if the telephone line can supportDSL communication and to indicate a fail state if the telephone line cannot support xDSL communication.
 2. The loop integrity test device ofclaim 1, wherein the second loop integrity test device couples to thetelephone line at the second point and is operable to complete the firstloop integrity test by receiving and evaluating the first test signatureand indicating whether the telephone line can support xDSL communicationbased upon evaluation of the first test signature and to independentlyinitiate the second loop integrity test by transmitting the second testsignature across the telephone line.
 3. The loop integrity test deviceof claim 1, wherein the evaluation unit is further operable to evaluatethe second test signature to determine physical characteristics of thetelephone line.
 4. The loop integrity test device of claim 3, whereinphysical characteristics of the telephone line comprise impedance of thetelephone line.
 5. The loop integrity test device of claim 3, whereinphysical characteristics of the telephone line comprise length of thetelephone line.
 6. The loop integrity test device of claim 1, whereinthe evaluation unit is further operable to evaluate the second testsignature to determine a loss of energy across the telephone line. 7.The test device of claim 1, wherein the generation unit is furtheroperable to generate the first test signature using an algorithm.
 8. Thetest device of claim 1, wherein the output device indicates the passstate and the fail state using at least one of a light emitting diode(LED) device, an audible alarm, an electronic register that can beaccessed by software, and an electronic signal provided to anothercomponent.
 9. The test device of claim 1, wherein the line interface isfurther operable to draw power from the telephone line sufficient tooperate the test device.
 10. A method for local loop integrity testingof digital subscriber line (xDSL) communications, the method comprising:initiating a test of a local loop telephone line by transmitting a testsignature from a first point on the local loop telephone line, the localloop telephone line forming a continuous electrically conductive pathwithout intermediate components between the first point and a secondpoint; receiving the test signature at the second point on the localloop telephone line; evaluating the received test signature at thesecond point to determine whether the local loop telephone line cansupport xDSL communication; and indicating whether the telephone linecan support xDSL communication.
 11. The method of claim 10, wherein thetest signature indicates initiation of the test to a device at thesecond point and provides sufficient information for the device tocomplete the test by indicating whether the telephone line can supportxDSL communication.
 12. The method of claim 10, wherein evaluating isaccomplished based upon changes to the test signature caused bytransmission across the local loop telephone line.
 13. The method ofclaim 10, wherein evaluating the received test signature furthercomprises determining physical characteristics of the telephone line.14. The method of claim 13, wherein determining physical characteristicsof the telephone line further comprises determining impedance of thetelephone line.
 15. The method of claim 13, wherein determining physicalcharacteristics of the telephone line further comprises determininglength of the telephone line.
 16. The method of claim 10, whereinevaluating the received test signature further comprises determining aloss of energy across the telephone line.
 17. The method of claim 10,wherein indicating includes is at least one of providing a visualdisplay of a pass state or a fail state, providing an electronic signal,and storing data in an electronic register.
 18. A loop integrity testdevice for digital subscriber line (xDSL) communication systems, thetest device comprising: means for initiating a test of a local looptelephone line by transmitting a test signature from a first point onthe local loop telephone line, the local loop telephone line forming acontinuous electrically conductive path without intermediate componentsbetween the first point and a second point; means for receiving the testsignature at the second point on the local loop telephone line; meansfor evaluating the received test signature at the second point todetermine whether the local loop telephone line can support xDSLcommunication; and means for indicating whether the telephone line cansupport xDSL communication.
 19. The test device of claim 18, wherein thetest signature indicates initiation of the test to a device at thesecond point and provides sufficient information for completing the testby indicating whether the telephone line can support xDSL communication.20. The test device of claim 18, wherein the means for evaluating isoperable to determine at least one of impedance of the telephone line,length of the telephone line, and a loss of energy across the telephoneline.
 21. A loop integrity test device for digital subscriber line(XDSL) communication systems, the test device comprising: a lineinterface unit operable to connect to and interface with a first pointon a twisted pair telephone line, the telephone line forming acontinuous electrically conductive path without intermediate componentsbetween the first point and a second point; an output device operable toindicate a pass state and a fail state; and a control unit comprising: ageneration unit operable to transmit a first test signature across thetelephone line for reception and evaluation at the second point by asecond loop integrity test device, the transmission of the first testsignature initiating a first loop integrity test, wherein the secondloop integrity test device couples to the telephone line at the secondpoint and is operable to complete the first loop integrity test byreceiving and evaluating the first test signature and indicating whetherthe telephone line can support xDSL communication based upon evaluationof the first test signature; and an evaluation unit operable to receivea second test signature transmitted across the telephone line, thesecond test signature originally generated independent of the first testsignature by the second loop integrity test device to initiate a secondloop integrity test independent of the first loop integrity test, theevaluation unit further operable to evaluate the second test signatureto determine whether the telephone line can support xDSL communication;the control unit operable to direct the output device to indicate a passstate if the telephone line can support DSL communication and toindicate a fail state if the telephone line can not support xDSLcommunication.